Duplicating objects for modeling buildings
You can use Block Modeling, first of all you need to be precise with the measurement, so I suggest you activate Snap and leave it on Increment, so that it uses the chosen unit for moving stuff in the next steps and to do all this in Orthographic View. Create blocks like the one in the picture that represent the basic elements you need to build your building, just make sure they have the same height and width (see picture below).

Now let's take a look at the Properties Panel: in the section shown in the picture below there are all the option that have to do with the actual geometric data of the selected object. If you click on the button on the right where there is the name of the geometric data (third picture) you can see the list of all geometric data you have in your scene and you can change the one regarding the selected object (in this case I renamed them for clarity so that the object's name matches its geometric data).


For example, if I select the Window Block in my viewport and change its geometric data to &quot;Door Block&quot; it actually transforms into a door block identical to the original one. Now they have the same geometric data so if you modify one the other gets modified too (which can be a downside depending of what you want to achieve).

So now with only just three different blocks you can create the base for any building you want by just copying one of the block (Shift+D), placing it where you want and changing its geometric data eventually. Keep in mind that doing this will results in a very long list of objects in the outliner so when you're done building and you are sure that they are placed correctly(see picture below) ,you can select every block and join them, but beware that this will result in overlapping faces where the blocks touch each other so you have to select everything in edit mode and click &quot;Remove Doubles&quot; (now called &quot;Merge by Distance&quot; in 2.8) on the Tool Shelf, and probably remove redundant geometry where is not needed anymore.

In no time you can already have something like this, and you can apply this method also when you create windows, doors, etc.